There is often a need to transfer messages from a traffic toll station to vehicles passing the toll station. Many vehicles are equipped with so called transponders able to communicate with the toll station. The transponder includes a transmitter and a receiver able to receive a message from the toll station and transmit information to the toll station. The communication can be DSRC-based (Dedicated Short Range Communication) where various standards exists, e.g. the CEN-standard (European Committee for Standardization) in the 5.8 GHz band. The transponder can be equipped with a configurable buzzer that can convey coded messages to the vehicle such as e.g.:                OK        Not OK        Contact operator.        
The message can be coded through a series of beeps or different tones.
The transponder can send an identification message to the to station thus allowing Electronic Fee Collection as the car is passing the to station without stopping.
The buzzers in transponders of today are generally simple piezo-electric buzzers. These buzzers do not have a sufficient sound quality for a voice message. To solve this problem more expensive buzzers have to be installed in the transponders. Even if high quality buzzers are installed in the transponders, a voice message from the transponder may be difficult to hear due to other sound sources in the vehicle as e.g. radio, TV or mobile phone.
FIG. 1 schematically shows a prior art solution of a vehicle mounted transponder 101 with an antenna 102 receiving a message from a toll station and outputting a coded message via a buzzer 103. The transponder is also capable of transmitting an identification message back to the toll station.
U.S. Pat. No. 6,344,804 B1 describes how a message from a toll station can be transferred to a vehicle unit in a vehicle and transferred to a voice message to be sent to an audio system in the vehicle. The transfer from the vehicle unit to the audio system is not described in detail. A transfer of a coded message to a synthesized voice signal is performed in the vehicle unit. When such a synthesized message is generated a switching unit is outputting the synthesized message to the audio system of the vehicle. This is a relatively complicated solution where modifications to the audio system have to be implemented.
There is thus a need for an improved solution for transferring messages from a toll station to a vehicle.